1. Field of the Invention
The present invention relates to a fusing roller apparatus for an electrophotographic image forming apparatus, and more particularly, to a fusing roller apparatus for an electrophotographic image forming apparatus, which can be instantaneously heated with low power consumption.
2. Description of the Related Art
In a general electrophotographic image forming apparatus such as a copy machine and laser beam printer, as an electrostatic charging roller adjacent to a photoreceptor drum rotates, a photosensitive material coated on the surface of the photoreceptor drum is uniformly charged. The charged photosensitive material is exposed to a laser beam scanned from a laser scanning unit (LSU) so that a latent electrostatic image is formed in a predetermined pattern on the photosensitive material. A developer unit supplies toner to the photosensitive material to develop the latent electrostatic image formed on the photosensitive material into a visible toner image. A predetermined transfer voltage is applied to a transfer roller which is put in contact with the photoreceptor drum at a predetermined force while the photoreceptor drum carries the toner image. In this state, as a print paper is fed in the gap between the transfer roller and the photoreceptor medium, the toner image formed on the photosensitive material is transferred to the print paper. A fixing unit which includes a fusing roller, instantaneously heats the print paper to which the toner image is transferred to fuse and fix the toner image to the print paper. In general, a halogen lamp is used as a heat source for the fixing unit. The halogen lamp is installed inside the fusing roller and heats the surface of the fusing roller to a target temperature with radiant heat.
In a conventional fusing roller apparatus of an electrophotographic image forming apparatus, which uses a halogen lamp as a heat source, the exterior surface of the fusing roller must generate heat; the fusing roller is therefore heated from the inside out by radiant heat from the halogen lamp. A pressure roller is located below the fusing roller. As paper carrying a toner image in a powder form passes between the fusing roller and the pressure roller, the paper is hot pressed by the predetermined force and the toner image is fused and fixed to the print paper by the heat and force from the fusing roller and the pressure roller.
A thermistor may be used for detecting and converting the surface temperature of the fusing roller into an electric signal and a thermostat may be used to cut off the power supply to the halogen lamp.
A conventional fusing roller apparatus which employs a halogen lamp as a heat source unnecessarily consumes a large amount of power, and needs a considerably long warm-up period when the image forming apparatus is turned on for image formation. In other words, after the application of power, a standby period follows until the temperature of the fusing roller reaches a target temperature, for example, for a few tens of seconds to a few minutes. I have found that with a conventional fusing roller apparatus, because the fusing roller is heated by radiant heat from the heat source, the rate of heat transfer is low. In particular, compensation for temperature variations due to a drop in the temperature of the heat roller caused by contact with a print paper is delayed, so that it is difficult to uniformly control the distribution of temperature along the axial length of the fusing roller. Even in a stand-by mode where the operation of the printer is suspended, power must be periodically applied so as to keep the temperature of the fusing roller constant, thereby causing unnecessary power consumption. Also, it takes a considerable amount of time to switch the fusing roller from its stand-by mode to an operating mode for image output, so that the resultant image cannot be rapidly printed.
An alternative design for a conventional fusing roller apparatus employs a heating plate placed in a lower portion of a flexible cylindrical film tube, with a pressure roller mounted underneath the heating plate. The film tube is rotated by a separate rotation unit and is locally heated and deformed at a part between the heating plate and the pressure roller. While this method of locally heating the film tube with a heating plate was thought to be advantageous in terms of low power consumption, it is unsuitable for high-speed printing.
Japanese Patent Application Nos. sho 58-163836 (Sep. 16, 1983); hei 3-107438 (May 13, 1991), hei 3-136478 (Jun. 7, 1991); hei 5-135656 (Jun. 7, 1993); hei 6-296633 (Nov. 30, 1994); hei 6-316435 (Dec. 20, 1994); hei 7-65878 (March 24, 1995); hei 7-105780 (Apr. 28, 1995); hei 7-244029 (Sep. 22, 1995); hei 8-110712 (May 1, 1996); hei 10-27202 (Feb. 9, 1998); hei 10-84137 (Mar. 30, 1998); and hei 10-208635 (Jul. 8, 1998) disclose heat-pipe equipped fusing roller apparatus.
Such fusing roller apparatus using heat-pipes can be instantaneously heated, thereby reducing power consumption. Fusing roller apparatus also have a short period of delay when switching between stand-by and a printing operation. In particular, the fusing roller apparatus disclosed in Japanese Patent Application Nos. hei 5-135656; hei 10-84137; hei 6-29663; and hei 10-208635 employ different types of heat sources at one end of the fusing rollers, that are positioned beyond the fixing areas. The arrangement of the heat source for each of these fusing roller apparatus increases the volume of the fusing roller apparatus and requires complex structures. Thus, there is a need to improve the structural complexity of such fusing roller apparatus.
The fusing roller apparatus disclosed in Japanese Patent Application Nos. sho 58-163836; hei 3-107438; hei 3-136478; hei 6-316435; hei 7-65878; hei 7-105780; and hei 7-244029 have their heat sources located within their fusing rollers, so that there remains a problem attributable to the increased volume of this apparatus described above. A plurality of local heat pipes, however, are installed for each fusing roller, thereby complicating fabrication and manufacture of the fusing roller apparatus. The local arrangement of the heat pipes moreover, causes temperature deviations between heat-pipe contact portions and heat-pipe non-contact portions.
To solve these and other problems in the art, it is an object of the present invention to provide an electrophotographic image forming apparatus and process.
It is another object to provide an improved fusing roller and fusing process.
It is still another object to provide a fusing roller apparatus for an electrophotographic image forming apparatus, in which local temperature deviation of a fusing roller is sharply reduced, thereby improving overall thermal distribution characteristics.
It is yet another object of the present invention to provide a fusing roller apparatus for an electrophotographic image forming apparatus, which is easy to manufacture and is designed to minimize any increase in the size of the fusing roller apparatus.
It is still another object to provide a fusing roller able to progress from its standby state to its printing state in a shorter period of time.
It is also an object to provide a more energy efficient electrophotolithographic process and apparatus.
It is a further object to provide a fusing roller, process for constructing a fusing roller and a process for fusing electrostatic images formed from toner onto a printable medium, with an assembly able to change the temperature of the fusing roller from room temperature to an operating temperature within a shorter period of time.
It is a still further object to provide a fusing roller, process for constructing a fusing roller and a process for fusing electrostatic images formed from toner onto a printable medium, with an assembly that is able to allow the temperature of the fusing roller to remain at room temperature during a standby operational period.
It is a yet further object to provide a fusing roller, process for constructing a fusing roller and a process for fusing electrostatic images formed from toner onto a printable medium, with an assembly that exhibits an improved thermal equilibrium and minimal local thermal differences on the cylindrical exterior surfaces of the fusing roller.
To achieve these and other objects of the present invention, in a first embodiment there is provided a fusing process and roller apparatus that may be practiced with a heat pipe that is hermetically sealed at both ends to maintain a vacuum within the interior cavity of the heat pipe. The interior cavity of the heat pipe contains a predetermined amount of a working fluid. The heat pipe is installed coaxially inside the hollow interior of a cylindrical fusing roller and a heat-generator is helically wound around the cylindrical exterior of the heat pipe, in the annular clearance between the heat pipe and the cylindrical interior surface of the fusing roller.